1. Field of Use
This invention pertains to storage apparatus and more particularly to storage apparatus used for processing segment descriptor information.
2. Prior Art
Today, many systems employ a combination of paging and segmentation features. One of the more well known of these systems is the MULTICS system. Such systems utilize segment descriptor words, each of which contain information pointing to the page table of the segment if the segment is known to reside in memory, the size of the segment and a descriptor field containing access control information. The number of bits for a segment descriptor word is relatively large, particularly where the system memory capacity is large or sophisticated security controls are utilized. For further information about the MULTICS system, reference may be made to the text "The MULTICS System: An Examination of its Structure", by Elliott I. Organick, Copyright 1972.
In order to store and access segment descriptor words, systems have used groups of memory locations or storage registers having the requisite number of bit positions. This requires the use of pairs of RAM chips to provide the desired storage register width. While this approach is suitable for many systems, it requires too much space and consumes too much power for systems implemented using very large scale integration (VLSI) chip technology. Also, in order to utilize the segment descriptor words, additional information may also have to be stored. This can increase RAM storage requirements adding to space and power consumption.
Accordingly, it is a primary object of the present invention to provide segment descriptor storage apparatus which is simple to construct in VLSI form and requires a minimum of space.
It is another object of the present invention to provide segment descriptor storage apparatus which consumes a minimum of power.